The invention relates to the continuous homogenization and mixing of plastic materials using axially parallel worm elements with the same pitch direction and near engagement with one another when driven in the same sense.
Such worm elements are known from German Offenlegungsschrift No. 2,003,593. Their special feature is that at each turn of a worm element, there is a sealing ridge which overarches the turn and is perpendicular to it. The external diameter of the sealing ridge corresponds to the diameter of the worm element. As a result, the pitch of the worm element is sealed in its throughflow direction. Because of the sealing ridge, a strong build-up of pressure takes place during each turn of the worm element. This initiates plastification of the material being processed. In order to give the sealing ridge of the neighboring worm element a necessary free space, the worm element has a corresponding recess at the position which moves past the sealing ridge as the worm element rotates. The recess interrupts the shear edge of the neighboring worm element, making it possible for the material being transported by the worm element to escape into a neighboring turn of that element. Consequently, the areas before the ridges and the recesses are the positions where the plastic materials essentially are acted upon.
Accordingly, it is an object of the invention to cause the positions of action on plastic materials, in the sense of homogenizing and mixing the materials, where the positions follow one another along the individual worm elements, to follow one another relatively densely.
Another object of the invention is to distribute the processing of the plastic materials as uniformly as possible over the respective length of the worm element, and in this way obtain a particularly homogeneous product.
Still another object of the invention is to shape the position of action in such a way that the action generally occurs in substantially the same manner.
A still further object of the invention is to avoid the undesirable effects which exist in the known devices. A related object is to avoid the particularly strong action at the ridges of known devices and, conversely the significantly weaker action through the recesses. Still another related object is to avoid action whose strength varies in alternation.